The present disclosure relates generally to components for reproduction and reprographic machines, such as copiers, printers, facsimile machines, bookmaking machines and any apparatus which performs a print outputting function. More particularly, the disclosure concerns improvements that extend the wear or fatigue life of certain components of these types of machines.
In one type of toner image reproduction machine, for example an electrostatic printing process machine, a photoconductive member is charged to a substantially uniform potential so as to sensitize the surface thereof. The charged portion of the photoconductive member is exposed to a light image of an original document being reproduced. Exposure of the charged photoconductive member selectively dissipates the charges thereon in the irradiated areas to record an electrostatic latent image on the photoconductive member corresponding to the informational areas contained within the original document.
At the imaging station, a document handling unit is positioned over a platen of the printing machine. The document handling unit sequentially feeds documents from a stack of documents to be copied. After imaging, the original document is returned to a document tray or through a duplex path.
After the electrostatic latent image is recorded on the photoconductive member, the latent image is developed by bringing a developer material into contact therewith. Generally, the developer material comprises toner particles adhering triboelectrically to carrier granules. The toner particles are attracted from the carrier granules to the latent image forming a toner powder image on the photoconductive member. The toner powder image is then transferred from the photoconductive member to a copy sheet. The toner particles are heated to permanently affix the powder image to the copy sheet.
The foregoing generally describes a typical black and white electrostatic printing machine. With the advent of multicolor electrophotography, it is desirable to use an architecture which comprises a plurality of image forming stations. One example of the plural image forming station architecture utilizes an image-on-image (IOI) system in which the photoreceptive member is recharged, re-imaged and developed for each color separation. This charging, imaging, developing and recharging, re-imaging and developing, all followed by transfer to paper, is done in a single revolution of the photoreceptor in so-called single pass machines, while multi-pass architectures form each color separation with a single charge, image and develop, with separate transfer operations for each color.
In either case, the toner image ordinarily is transferred unfused onto a copy sheet of paper, which is then picked up by a transport mechanism (a prefuser transport) for delivery to a fuser assembly where the toner is heated and fused to make a finished copy. Conventional pre-fuser transport mechanisms typically use rotating belts stretched between a drive shaft and an idler shaft with perforations in the belts that allow vacuum pressure from a blower to be drawn through holes in a plate below the belts, and through the belts to the sheet. The vacuum pressure assists each sheet of paper that has an image on it via electrically charged toner particles, to be pulled off the photoreceptor and acquired on the pre-fuser transport, without disturbing the unfused image on the sheet, especially in the transfer zone.
A conveyer then typically advances the copy sheet to a fusing station that includes a fuser assembly which permanently affixes the transferred toner powder image to the copy sheet. The fuser assembly often includes a heated fuser roller and a pressure roller with the powder image on the copy sheet contacting the fuser roller. The fuser roller may be internally heated by a quartz lamp. Release agent, stored in a reservoir, is pumped to a metering roll. A trim blade trims off the excess release agent. The release agent transfers to a donor roll and then to the fuser roll. The release agent helps release the copy paper from the fuser roll after the image has been fused.
After fusing, the copy sheets may be fed through a decurler that bends the copy sheet in such a way that the sheet curl produced during the fusing operation is substantially reduced. The sheet is then advanced to a duplex solenoid gate that guides the sheet to a finishing station or to a duplex tray. The duplex tray provides an intermediate storage for those sheets that have been printed on one side and on which an image will be subsequently printed on the second, opposed side thereof—i.e., the sheets being duplexed. In order to complete duplex copying, the simplex sheets in tray are fed back to the transfer station for transfer of the toner powder image to the opposed sides of the copy sheets. The duplex sheet is then fed through the same path as the simplex sheet to be advanced to the finishing station. Copy sheets are fed to the transfer station from a high speed feeder tray as well as from secondary trays. In many machines, a vacuum feed belt feeds successive uppermost sheets from the trays to the transfer station.
Further details of this typical reproduction machine can be garnered from U.S. Pat. No. 6,314,268, which issued to the assignee of the present application on Nov. 6, 2001, the disclosure of which is incorporated herein by reference, particularly the disclosure related to FIG. 1 of that patent.
In many reproduction machines, a photoreceptor cleaning apparatus is provided to remove residual image forming toner from the surface of the photoreceptor. A typical cleaning apparatus includes a flexible element that rides on the photoreceptor surface as the surface passes by the element. The flexible element may be a brush or a blade, such as the blade disclosed in U.S. Pat. No. 4,970,560, which issued to the assignee of the present application on Nov. 13, 1990, the disclosure of which is incorporated herein by reference.
In most reproduction machines, the fusing station is the critical element that fixes the reproduced image on the transfer or copy sheet. Most fusing stations include the heated fuser roll and the pressure roller described above. Roll-type fusers fall into two general categories: low gloss, typically found in black and white reproduction engines; and high gloss, typically used in color engines. Low gloss fusers produce images with a limited dynamic range, while high gloss fusers can usually achieve a dynamic range of 75-90 to give the reproduced image “depth”. Dynamic range is especially important for color reproduction, where the emphasis is often on creating photographic quality prints.
High gloss reproduction is complicated by consumer desire for high copy rates. With higher sheet feed and copy rates, the sheet or substrate necessarily spends less time at any one station of the reproduction machine, including the fusing station where the toner image is fixed on the sheet. This reduced processing time frequently leads to non-uniform gloss on the sheet, which is an undesirable phenomenon. In order to maintain as uniform a gloss as possible, the fuser roll must conform to the surface of the substrate or sheet. Low spots on the sheet make poor contact with the fuser roll and therefore acquire little gloss.
On the other hand, a fuser material that is soft enough to conform to the substrate surface is susceptible to high wear rates. To provide a “soft” roll with a harder wear resistant characteristic, many color fusers overcoat a silicone layer with a thin VITON™ rubber layer. This material is a fluoroelastomer produced by E.I. du Pont de Nemours & Co. One example of a fuser roll of this design is disclosed in U.S. Pat. No. 5,807,631 (the '631 Patent), which issued to the assignee of the present application on Sep. 16, 1998. The entire disclosure of this patent is incorporated herein by reference. In particular, them '631 Patent discloses a multi-layered nip forming fuser roll (NFFR) in which the heated roll includes a substantially rigid core member having a radiant quartz heater disposed therein. The heating element radiates heat to the cylinder which is conducted to the outer layers of the roll. The first layer of the roll is a heat conductive silicone rubber layer. This layer is followed by two layers of VITON™, in which the innermost layer is thermally conductive and the outer layer is relatively non-conductive. The relatively conductive layers (i.e., the silicone and innermost VITON™ layers) are rendered conductive by the use of appropriate metallic and/or non-metallic fillers. The fillers are integrated into the layers in a manner that does not disturb the deformability or “softness” of the layers.
Since VITON™ is much harder than the underlying silicone, the addition of the VITON™ material helps extend the life of the fuser roll. However, the VITON™ material is typically more expensive than traditional coating materials used in reproduction machines. Moreover, use of the VITON™ material can make color fusers much more expensive to operate than the typical low gloss black and white fuser. There is consequently a need for a fuser roll construction that is capable of achieving high gloss reproduction at a cost that approximates the low gloss engines.
Wear and expense are also critical concerns for other high frequency service components of a high speed reproduction or printing machine. As described in the '631 Patent, the fuser roll includes a release agent management (RAM) system that applies a release agent to the surface of the fuser roll to prevent adherence of the substrate to the fuser roll. The RAM system disclosed in the '631 Patent utilizes a wiper blade formed of VITON™ to create a uniform layer of the release agent on a metering roll. Like the fuser roll, the wiper blade wears over time and must be replaced. Similar cleaning blades are used to clean the photoreceptor and certain feed rolls. The feed rolls themselves are also high frequency service components in a typical reproduction machine.
There is a continuing need to improve the life of the typical service components of reproduction machines, especially high speed machines. In addressing this need, it is also important to reduce the overall acquisition and operating costs of the machine.